The present invention relates to the strength testing of sheet materials, and more particularly to a pneumatic system having a high pressure air source which by way of a valve feeds into a chamber having one wall consisting of the sheet material to be tested. In general, the present invention relates to sheet materials. However, the following discussion refers to the specific sheet material of paper.
Paper is produced in various grades to suit various applications. It is, of course, important that paper be strong enough to perform its intended function. To ensure adequate strength, and thus satisfactory performance, paper sheets must be tested for strength.
Paper commonly is produced in bulk in a continuous sheet. The sheet is wound in reels at the end of the manufacturing process, and immediately after one reel is finished, another reel is begun. Often it is desirable to measure the strength of the paper during the manufacturing process, so that if paper strength is not satisfactory, process controls can be adjusted accordingly.
Prior art devices for measuring the strength of paper ruptured the paper by projecting a solid object through the plane of the paper. Such devices are not easily adapted to use during the manufacturing process, if at all, because the solid object remains projected through the plane of the paper and would continue to tear the paper sheet as the paper moves past the strength tester. These prior art devices cannot be used until after completion of the manufacturing process.
For instance, the Mullen test, also known as the burst pressure test, uses a rubber diaphragm and liquid pressure to rupture the paper. In this test, the paper sample is clamped between two circular clamping rings which have a specific standard inner diameter. A rubber diaphragm is placed on one side of the sheet sample, and liquid pressure is applied until the paper ruptures. The pressure required to rupture the paper is called the "burst pressure" and is commonly used in the paper industry to specify strength.
Since the prior art strength testers are not used until after completion of the manufacturing process, paper production is inefficient. If process controls require adjustment in order for strength requirements to be met, the need for this adjustment is not known until after the paper reel has been completely manufactured, and the sheet has been tested in the lab. This process is time-consuming and costly. Paper with inadequate strength characteristics continues to be produced until lab tests are made and process controls can be adjusted.
The present invention overcomes the disadvantages of the prior art, for it provides a means for measuring sheet strength during the manufacturing process.